1. Field of the Invention
The invention relates to the real time processing of graphic cell specifications to generate printed vector graphics. More particularly, the invention relates to a cell specification processor which processes a graphic cell specification for a particular scan line and then modifies the cell specification by substituting new values for several identifier fields. These new values allow the modified cell specification to be recirculated and used to calculate pixel data for a subsequent scan line.
2. Description of the Prior Art
This application relates to and is an improvement of a copending application entitled REAL TIME CELL SPECIFICATION PROCESSOR by William Koos, Timothy Geis, and Richard M. Rudy, which has been filed of even date herewith, commonly assigned and incorporated by reference. That application describes a processor which generates character fonts and logos from cell specifications. The current application discloses a cell specification processor which can process graphic cell specifications to generate vector graphics. The generated vector graphics (i.e. diagonal lines) can be used as elements in printing circles or any desired design.
The invented cell specification processor utilizes a technique which eliminates cumulative error. Prior art methods use rise over run calculation methods which will result in cumulative error. Under the prior art method, for each successive scan line, an image is generated using a constant horizontal displacement, i.e. for each scan line drop the horizontal location of the pixel image is moved over a constant horizontal displacement. In an analogue system the actual horizontal displacement of the pixel image can exactly equal the desired constant horizontal displacement and no cumulative error will result. However, when the horizontal scan line is divided into a descrete number of dot locations a constant horizontal displacement ratio (e.g. a run of three dots for a rise of one scan line) will result in an accumulating error. This is because the horizontal displacement per scan line is not a constant for the total length of a line segment when we approximate the line to the nearest discrete dot position.